Benzalkonium Chloride Adaptation Increases Expression of the Agr System, Biofilm Formation, and Virulence in Listeria monocytogenes.

Xiaobing Jiang,Siyu Ren,Tao Yu,Shuxing Qiu,Rui Kang,Xiaojie Jiang,Congyi Jiang

doi:10.3389/fmicb.2022.856274

Xiaobing Jiang, Siyu Ren + Show 5 more

Open Access

https://doi.org/10.3389/fmicb.2022.856274

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Abstract

Benzalkonium chloride (BC) is widely used for disinfection in food industry. However, prolonged exposure to BC may lead to the emergence of BC adapted strains of Listeria monocytogenes, an important foodborne pathogen. Until now, two communication systems, the LuxS/AI-2 system and the Agr system, have been identified in L. monocytogenes. This study aimed to investigate the role of communication systems in BC adaptation and the effect of BC adaptation on two communication systems and the communication-controlled behaviors in L. monocytogenes. Results demonstrated that the Agr system rather than the LuxS system plays an important role in BC adaptation of L. monocytogenes. Neither luxS expression nor AI-2 production was affected by BC adaptation. On the other hand, the expression of the agr operon and the activity of the agr promoter were significantly increased after BC adaptation. BC adaptation enhanced biofilm formation of L. monocytogenes. However, swarming motility was reduced by BC adaptation. Data from qRT-PCR showed that flagella-mediated motility-related genes (flaA, motA, and motB) were downregulated in BC adapted strains. BC adaptation increased the ability of L. monocytogenes to adhere to and invade Caco-2 cells but did not affect the hemolytic activity. Compared with the wild-type strains, the expression levels of virulence genes prfA, plcA, mpl, actA, and plcB increased more than 2-fold in BC adapted strains; however, lower than 2-fold changes in the expression of hemolysis-associated gene hly were observed. Our study suggests that BC adaptation could increase the expression of the Agr system and enhance biofilm formation, invasion, and virulence of L. monocytogenes, which brings about threats to food safety and public health. Therefore, effective measures should be taken to avoid the emergence of BC adapted strains of L. monocytogenes.

Highlights

Disinfection is an important operation in food industry, which can avoid the microbiological contamination of food products and reduce the risk of foodborne diseases (Pricope et al, 2013)
To investigate the role of two communication systems in Benzalkonium chloride (BC) adaptation of L. monocytogenes, the gene deletion mutant strains of luxS and agr derived from HL28 were constructed in this study
After BC adaptation, HL28ΔluxSBCA showed the Minimum inhibitory concentrations (MICs) of BC with 14 μg/ml, the same value as that of HL28BCA; the BC MIC of HL28ΔagrBCA was lower than that of HL28BCA (Table 3). These results indicate that the Agr system rather than the LuxS system plays an important role in BC adaptation of L. monocytogenes

Summary

Introduction

Disinfection is an important operation in food industry, which can avoid the microbiological contamination of food products and reduce the risk of foodborne diseases (Pricope et al, 2013). The causative agent of listeriosis in humans and animals, represents a major foodborne pathogen. It can be found in a wide variety of raw and processed foods (Montero et al, 2015; Shamloo et al, 2019; Falardeau et al, 2021). Previous studies have reported the emergence of adaptation to BC (it refers to “adaptive resistance to BC”) when L. monocytogenes are frequently exposed to sublethal concentrations of BC (Aase et al, 2000; Lundén et al, 2003; Romanova et al, 2006). After BC adaptation, L. monocytogenes exhibits cross-adaptation to other disinfectants and to antimicrobial agents, such as cephalosporin, ciprofloxacin, gentamicin, kanamycin, and ethidium bromide (Romanova et al, 2006; Rakic-Martinez et al, 2011; Yu et al, 2018)

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